1) Field of the Invention
The present invention relates to elastomeric expansion joints for coupling tubes. In certain situations, the tubing has critical points of higher pressures, movements and temperature, and tends to expand and cause disengagement or even breakage due to fatigue of the tubes. In order to prevent such drawbacks, elastomeric expansion joints are used either between tube segments or between a tubing portion and some type of equipment, so as to absorb the movements to which they are subjected.
Movements to be absorbed by elastomeric expansion joints include, for example, axial movements (increase in the distance between determined tube segments), lateral movements (disagreement between the central axes of the tubes interconnected by the joint), angular movements and vibrations to which the tubes are subjected. Movements can also result when these tubes are coupled to pieces of equipment that operate under varied conditions, such as temperature and pressure.
Essentially, the elastomeric expansion joints comprise a tubular elastomeric body, for example, manufactured from Cloroprene, Nitrilo, EPDM, Natural, Hypalon, etc. according to the application need. They may also comprise inner coatings of PTFE (polytetrafluoretylene) for solving the different operational loads.
In order to meet the stresses provoked by the high pressures inside the tubes that are coupled, one usually provides internal reinforcements with fabrics of synthetic material in conjunction with reinforcement wires, which are aimed at guaranteeing greater strength for operation under internal pressure or even in situations of vacuum.
2) Description of Related Art
Some known solutions are provided with metallic reinforcements inside the elastomeric structure, so that the rupture pressures can be higher.
One of the solutions found in the prior art is described on U.S. Pat. No. 3,580,616. This document discloses an expansion joint reinforced with wound wires for increasing the strength of the assembly. In order to prevent movement of the wires, the latter are enveloped by a rubber mass and optionally accommodated on a layer of a more resistant type of rubber. With this solution, a reinforcement in the joint is achieved, without, however, resulting in a construction resistant to high pressures. One of the problems of this solution is that the spacing between the wires, as well as the support thereof on the rubber, may have the result that the wires move within the rubber throughout the use of the joint and may break when they go through the joint wall.
Another solution found in the prior art is described in U.S. Pat. No. 1,696,435. This document discloses an expansion joint comprising metal rings pressed from above and from below by layers of web, thereby to prevent the respective movement and direct contact with the more flexible rubber layer. One of the drawbacks of this type of construction lies in that the metal rings impart little flexibility to the joint and are of considerable thickness, which may cause fatigue of said webs in the event of movement of the whole assembly.
A prior technique is also known and described in U.S. Pat. No. 3,429,592. This solution follows the same concept of the documents cited above and comprises essentially metal rings accommodated inside layers of a more resistant type of rubber, defining a support to prevent movement of the rings. This solution, however, imparts little flexibility to the joint and results in a piece of considerable thickness, which may cause fatigue of the joint.
Other solutions may be found in documents JP 2022039, U.S. Pat. Nos. 3,051,512, 3,305,251, 2,692,782 and 4,101,150, which describe solutions that comprise a resistant enveloping element and arrangements to prevent it from moving. The enveloping elements are configured as rings and positioned separated from each other, causing wear of the material that envelops them. This separate positioning of the rings cause them to be in direct contact with the enveloping material, which is usually rubber or webs and, with the passing of time and the continuous movement of the joint, result in fatigue of the piece.
Another solution that tries to solve the problem of resistance to high pressures on expansion joints may be found in document U.S. Pat. No. 3,039,795, which discloses a flexible expansion joint that comprises a spiral metal element surrounding the joint. This spiral element is positioned around or inside the polyurethane layer, which, throughout the use of the joint, causes fatigue of the material, which is deformable.
Other solutions foresee the use of external flanges, on which the rubber portion of the joint will rest in order to bear higher pressures. According to these techniques, the external flanges rest on the external portions of the joint and extend along the outer surface of the joint, along the respective external portion, as far as the more central arched portion, thus forming a metallic cylindrical portion that lines the joint.
Although this solution results in a joint that supports higher pressure, its flexibility is very impaired, which, in turn, results in low performance in absorbing vibrations, compression, angular movement, etc. Moreover, in addition to the low performance of this type of joint as far as the flexibility aspect is concerned, the use of this type of external flanges bring extra cost for the final product.